As the size of portable wireless devices is decreasing, the space for receiver antennas thereof is also decreasing. Japanese Unexamined Patent Application Publication (JP-A) No. 2001-339226 describes an antenna having improved antenna characteristics and which can be effectively used in a limited space.
The structure of the antenna described in JPA-2001-339226 will now be described with reference to FIG. 1. In FIG. 1, a conductive tabular auxiliary element 53 is attached to an antenna element including a dielectric 51 and an electrode pattern 52 formed on the dielectric. The electrode pattern 52 is connected to a feeding point 55.
According to the antenna described in JP-A-2001-339226, the resonant frequency of the antenna is reduced due to an effect of wavelength shortening obtained by using the dielectric element and an effect of the conductive tabular auxiliary element 53 connected thereto, and as a result, the antenna characteristics can be improved while the limited space for the antenna is effectively used.
However, the antenna described in JP-A-2001-339226 requires the conductive tabular auxiliary element 53 in addition to the dielectric 51 in order to operate at a desired frequency. Moreover, when the antenna described in JP-A-2001-339226 is of a multiband type that operates with desired fundamental and harmonic waves, the antenna also requires the tabular auxiliary element 53 so that the frequencies of the fundamental and harmonic waves are not changed. That is, the antenna needs to be designed on the premise that the tabular auxiliary element 53 exists.